Shaders & Noise

Does anyone have a link to a tutorial for adding noise, dirt and such to texture
maps to make it look more realistic?...

i'm familiar with the bump and displacement now, but i don't quite know how to
do these concepts yet: shading, baking light into objects and adding noise on a
texture map..

plz, i'm searching my ass off for a decent tutorial, can't seem to find any?...